The present invention relates to a ventilatory assister for various types of respiratory failure patients.
A negative pressure type artificial ventilator which assists physiological negative pressure respiration is useful for patients having chronic respiratory failure such as pulmonary fibris, pulmonary emphysema, secondary disease after pulmonary tuberculosis, etc., and for patients having neuromyopathy malady, or the like.
An extra thoraco-abdominal negative pressure artificial ventilator, or so-called iron lung was made in 1927 by Drinker, wherein a respiratory failure patient is laid within the dome the interior of which is then made negative in pressure to expand the thorax, inflate the lung and assist the respiration. However, the iron lung is volumious, heavy, immovable and inefficient. In the 1950's, a positive pressure artificial ventilator which sends oxygen via a tube inserted in the windpipe had been prevailing so that an iron lung became to be used scarcely.
In 1930's, another method of also expanding the thorax to assist respiration had been tried by mounting the dome only on the thoraco-abdominal. However, it was difficult to air-tightly contact the bottom peripheral portion of the dome for various patients whose posture are different each other. The efficiency thereof was inferior to that of an iron lung.
Recently, attention has been drawn to some disadvantage of a positive pressure artificial ventilator, particularly for chronic respiratory failure patients. Namely, such patients have a clear consciousness so that they feel a pain against endotracheal intubation used with the positive pressure artificial ventilator. In addition they can not eat food and have a conversation. Another disadvantage is that the lung may be damaged by the positive pressure, infectious disease via the windpipe may occur, and so on. Further, there is also a problem that since the patient has long relied upon the artificial ventilator, he or she cannot dispense with it after recovery, or the number of respiratory assistances becomes necessary to be reduced gradually over a long period.
In view of the above background, the negative pressure artificial ventilator has taken a favorable turn in the 1980's. An extra thoraco-abdominal negative pressure artificial ventilator has been developed, whose dome is made of a light material and can be attached to the patient body (e.g., refer to "Respiratory Care", 27(3), pp.217 to 275, 1982, "Clinical Thoracic Surgey", 4(2), pp.153 to 157, 1984, "Respiration and Circulation", 34(4), pp.407 to 411, 1986). The ventilators described in the above articles, however, are arranged to mechanically assist respiration by using a constant respiration timing. Therefore, the constant timing may mismatch the timing which a patient desires to have, so that a so-called fighting condition appears which hurts patient's feelings.
Also, a method of assisting respiration in accordance with a patient's spontaneous respiration has been made also for a negative pressure artificial ventilator, e.g., by picking up changes in pressure and temperature caused by respiration at the vicinity of the patient's narises (refer to "New Eng. J. of Med.", 268, 61, 1963, "Japanese Patent Laid-open Pulbication" JP-A-x61-176348, "Respiration", 6(3), 254, 1987). However, this respiration assistance does not always follow the patient's real physiological intention and is not practically realized up to date.
The method of assisting respiration in accordance with a respiration rhythm set in the conventional ventilator is none the less unnecessary because of the following reasons: For those patients with weak respiration from which the expiration and inspiration timings are difficult to be picked up, such as patients with neuromyopathy malady like myotonic dystrophy, and for those patients under apnea, it is requisite to carry out mechanical respiration assistance in accordance with the respiration rhythm previously set by the ventilator. Further, for those patients whose spontaneous respiration becomes feeble or who get into apnea because of a sudden change of patient's health condition, it is requisite to immediately change to respiration assistance by the respiration rhythm previously set by the ventilator.